Question

A driver of a car approaching a vertical wall notice that the frequency of his car horn has changed from 440 to 480 Hz when it gets reflected from the wall. Find the speed of the car if the speed of the sound is $300m{s}^{-1}$

• A. $16.3m{s}^{-1}$
• B. $15.3m{s}^{-1}$
• C. $14.3m{s}^{-1}$
• D. none of these

Answer 1

Answer: (C)

$14.3m{s}^{-1}$

Let the velocity of car be $u$
Then $480=\frac{v+u}{v-u}440$ or
$\frac{48}{44}=\frac{v+u}{v-u}oru=\frac{330}{23}=14.3m{s}^{-1}$